Porous metal bodies having a three-dimensional network structure have been used in a wide range of applications, such as various filters, catalyst supports, and battery electrodes. For example, Celmet (manufactured by Sumitomo Electric Industries, Ltd., registered trademark) made of nickel has been used as an electrode material for batteries, such as nickel-hydrogen batteries and nickel-cadmium batteries. Celmet is a porous metal body having continuous pores and characteristically has a higher porosity (90% or more) than other porous bodies, such as metal non-woven fabrics. Celmet can be manufactured by forming a nickel layer on a surface of the skeleton of a porous resin having continuous pores, such as urethane foam, decomposing the resin expansion molded body by heat treatment, and reducing the nickel. The nickel layer can be formed by performing a electrical conduction treatment of applying a carbon powder to the surface of the skeleton of the resin expansion molded body and then depositing nickel by electrodeposition.
Aluminum has excellent characteristics, such as conductive property, corrosion resistance property, and lightweight. For use in batteries, for example, aluminum foil to which an active material, such as lithium cobalt oxide, is applied has been used as a positive electrode of lithium-ion batteries. In order to increase the capacity of a positive electrode, an aluminum body can be processed into a porous body having a large surface area, and the inside of the aluminum body can be filled with an active material. This allows the active material to be utilized even in an electrode having a large thickness and improves the active material availability ratio per unit area.
As a manufacturing method of porous aluminum, Patent Literature 1 describes a method for subjecting a plastic substrate having an inner continuous space and a three-dimensional network to an aluminum vapor deposition process by an arc ion plating method to form a metallic aluminum layer having a thickness in the range of 2 to 20 μm. Patent Literature 2 describes a method for forming a porous metal body, including forming a film made of a metal (such as copper) on the skeleton of a resin expansion molded body having a three-dimensional network structure, the metal having an ability to form an eutectic alloy at the melting point of aluminum or less, applying an aluminum paste to the film, and performing heat treatment in a non-oxidizing atmosphere at a temperature of 550° C. or more and 750° C. or less to evaporate the organic constituent (resin foam) and sinter the aluminum powder.
Since aluminum has high chemical affinity to oxygen and a lower electric potential than hydrogen, the electrodeposition in a plating bath containing an aqueous solution is difficult to perform in aluminum plating. Aluminum electrodeposition has been studied in a plating bath containing a non-aqueous solution, in particular, a plating bath containing an organic solvent. For example, as a technique for plating a metal surface with aluminum, Patent Literature 3 discloses an aluminum electrodeposition method characterized in that a low melting composition, which is a blend melt of an onium halide and an aluminum halogenide, is used in a plating bath, and aluminum is deposited on a cathode while the water content of the plating bath is maintained at 2% by weight or less.